This invention relates to a method and apparatus for casting parts and investment models from fluid compositions which solidify when exposed to actinic radiation. The compounds are solidified within a mold by irradiating the photocurable compounds as they enter the mold or through openings in the body of the mold. The invention is effected by using compounds from the class of photo-hardened fluids including those which 1) conduct the actinic radiation they are responsive to whereby the radiation travels throughout the body of the part being cast and/or 2) undergo a hardening chain reaction which is triggered by exposure to actinic radiation.
Photocurable resins have been used to produce three-dimensional parts and patterns for investment casting. The techniques predominantly used are stereolithography wherein a part or model is created by the slow accretion of layers cured by computer controled laser beams and by direct casting using relatively thin walled molds which are transparent to the actinic radiation.
One example of using stereolithography to produce three-dimensional patterns for investment casting is U.S. Pat. No. 4,844,144 issued to E. Murphy et al., on Jul. 4th, 1989. This system utilizes a light curable ethylenically unsaturated liquid material mixed with an inert thermoplastic material which is cured layer by layer as taught by Hull in U.S. Pat. No. 4,575,330.
The high cost and technical complexities inherent in the Hull process are eliminated by using a direct casting technique such as taught by S. Nakamura, et al. in U.S. Pat. No. 5,990,190. In this system, an actinic radiation transparent mold is surrounded by sources of curing radiation which penetrate the mold from six directions. The need to completely surround the mold with radiation greatly increases the complexity and cost of the process. Furthermore, the need to create the master mold from a radiation transparent material imposes severe limitations on the structural integrity of the mold and limits the geometry of the end product, i.e. the casting.
A primary objective of the present invention is to provide a method and apparatus for casting a part or a sacrificial model for investment casting from an actinic radiation curable material which is cast and cured in a mold that does not have to be transparent.
Another objective is to provide a method for casting a radiation curable material incorporating a photoinitiator wherein the material is cured in the mold by a single source of radiation.
A still further objective of the invention is to provide a method for casting an actinic radiation curable material by irradiating the material as it is being pored or injected into the mold.
Another objective of the invention is to photocure material within a mold by irradiating the material through the sprue hole.
A further objective is to cure material within a mold by transmitting curing radiation through one or more openings in the mold, such as vents, whereby curing radiation is transmitted through the total volume of mold cavity via the radiation transparency of the casting media.
Other objects, features and advantages of this invention will be apparent from the drawings, specification and claims which follow.
The present invention teaches a process and apparatus for casting three-dimensional parts and sacrificial models from a class of casting compounds which are solidified by actinic radiation. The class of casting compounds include, 1) compounds which act as conduits for the actinic radiation during and/or after hardening and 2) compounds which are hardened by an actinic radiation induced chain reaction throughout the body of fluid casting compound. These compounds allow the part being cast to be cured within molds that are opaque. The apparatus consists of an actinic radiation source positioned to irradiate the casting compound, which incorporates it photoinitiator, as it enters the mold and/or radiate into the mold cavity through the sprue hole, windows and/or venting holes to effect the solidifying process.